This invention relates to a method for removing odor components from a polyphenylene ether resin. More particularly, this invention relates to a method for removing odor components from a polyphenylene ether resin by extracting the resin with a ketone.
Polyphenylene ethers, also known as polyphenylene oxides, are a class of polymers widely used in industry, especially as engineering plastics in applications requiring toughness and heat resistance. In recent years, an increasing interest has developed in using polyphenylene ethers in food packaging applications.
In many of these food packaging applications, it is essential that the polyphenylene ether be free of materials which are volatile, have undesirable odors or would otherwise harm the food. Materials which contribute to the undesirable odor and taste of polyphenylene ether resins include 2,4,6-trimethylanisole, 7-methyldihydrobenzofuran, dihydrobenzofuran, 2,6-dimethylcyclohexanone, and 2-ethylhex-2-enal, all of which are byproducts formed in the synthesis of the substituted phenols from which the polyphenylene ethers are prepared. Of these materials, 2,4,6-trimethylanisole and, to a lesser extent, 7-methyldihydrobenzofuran, appear to be the predominant odor components in polyphenylene ether resins. Other materials contributing to the odor and taste of polyphenylene ether resins include dialkylamines, e.g., di-n-butylamine, and unsaturated amines, which are components of the catalyst used in the preparation of the polyphenylene ethers. The amines are generated when polyphenylene ether is extruded.
Currently, commercial polyphenylene ether is purified by a semicontinuous precipitation from toluene with methanol, removing quinones, other color bodies, catalyst residues and low oligomers from the resin. However, this purification process does not substantially remove the odor components in the polyphenylene ether for two reasons. First, the solvents used to make polyphenylene ether and to precipitate and wash it are recycled which results in a buildup of odor components to a steady state level. Second, methanol, which is used to wash the polyphenylene ether resin, is a relatively poor liquid for removing 2,4,6-trimethylanisole and 7-methyldihydrobenzofuran. As a result, commercial polyphenylene ether may currently be contaminated with these odor components.
Some of these odor components , such as 7-methyldihydrobenzofuran, dihydrobenzofuran, 2,4,6-trimethylanisole, and 2,6-dimethylcyclohexanone, as well as some of the amines, can be removed by vacuum venting, but it has been found that sufficient amounts of these odor components still remain after the vacuum venting process to have a discernible odor.
Thus, a need still exists for a method which substantially removes odor components from polyphenylene ethers.